New Research


Chemical Approach to Life Science

Chemical Synthesis of Damaged DNA and Its Application to DNA Repair Studies

Professor: Shigenori Iwai, Associate Professor: Isao Kuraoka, Assistant Professor: Junpei Yamamoto

   DNA (deoxyribonucleic acid) is a biopolymer that contains and transfers genetic information, and its function depends on the formation of the base pairs between adenine and thymine and between guanine and cytosine. The chemical structure of DNA is sometimes altered by chemical reactions. This structural change, which is called damage, induces mutagenesis and causes a cell to become cancerous. However, living organisms have many types of proteins that repair various DNA lesions.
   We are developing the methods for the chemical synthesis of DNA containing damaged nucleobases, and studying DNA repair using the synthetic DNA. The chemical synthesis of DNA was established nearly 30 years ago, but it is not easy to incorporate a particular lesion into DNA. Only few groups in the world have been tackling this study, and we successfully developed original methods to incorporate several types of ultraviolet-induced and oxidative lesions into DNA. Some of the damaged bases contain chiral carbon atoms, which are important for recognition by proteins. We also have succeeded in the selective synthesis of the stereoisomers of damaged bases. Since these damaged-DNA fragments are useful for biological studies, they are used as collaborative studies all over the world.
   Recently, we are synthesizing more useful DNA in combination with other modifications. One example is a fluorescent sensor for the detection of DNA repair in cells. We synthesized a hairpin-type DNA bearing a fluorophore and a quencher at the ends. This DNA was partially modified so that it was not degraded by nucleases, i.e. enzymes that hydrolyze DNA, and contained an oxidatively-damaged base. It was expected that fluorescence would be observed when this sensor was transfected into cells, because the cellular base-excision-repair enzyme would remove the damaged base and cleave the DNA strand. Actually, fluorescence was emitted from the nuclei, which contained the enzyme, whereas fluorescence was not detected for the same type of DNA without the damaged base.

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